This invention relates in general to weatherstrips, and more particularly to an improved weatherstrip of the type having a sealing body attached to an elongated backing strip, for installation, for example, in a slot, the improved weatherstrip having friction reducing self-aligning grooves formed in the backing strip.
Weatherstrips in which a sealing body is attached to a longitudinally extending backing strip have been widely used for many years. Among the popular and effective weatherstrips of this type is the weatherstrip described in U.S. Pat. No. 3,175,256 of R. C. Horton issued Mar. 30, 1965, the disclosure of which is incorporated herein by reference.
In the manufacture of weatherstrip and similar weatherstrips, a backing or substrate which may be formed from polypropylene yarns, for example, is woven in a loom in a width sufficient to form a multiplicity of parallel elongate weatherstrip elements. During the weaving operation, a plurality of spaced apart parallel pile strips is inserted into the backing and is arranged to project upwardly therefrom to form parallel rows of sealing bodies. Typically, the pile rows are formed from yarns such as single or multiple filament polypropylene yarns that have preferably been treated with silicone, and stabilized against degradation by ultraviolet radiation, so as to have a long life in out of door applications. Following the weaving and pile insertion operations, a suitable plastic material, such as polypropylene is extruded onto the substrate, particularly onto the face of the substrate opposite that from which the pile rows project. This step secures the pile in place, since the pile yarns extend through the substrate, and portions thereof appear on the back surface of the substrate; increases the rigidity of the substrate; and permits the substrate to be slit between the pile strips without fraying.
After the extrusion step, the substrate is slit between the pile strips to form individual lengths of weatherstrip, each consisting of a plastic coated backing strip or substrate with a sealing body upstanding therefrom. Preferably, a barrier strip of moisture impervious, flexible sheet material, such as polypropylene for example, is positioned within the pile strip running the length thereof, and is secured to the substrate or sealing body for example, by heat sealing. More recently, in U.S. Pat. No. 4,288,483, the disclosure of which is incorporated herein by reference, Miska et al have described a weatherstrip of the type just described, in which the flexible backing or substrate of the weatherstrip is fabricated of woven strands of either a thermoplastic material and a thermal setting material; two thermoplastic materials that have different melting points; or a thermoplastic material and some other material having a higher melting point. The pile strips which are composed of resisient fibers, can be woven into the substrate in the same way just described. However, instead of then having to extrude a suitable plastic material onto the back of the substrate, heat is simply applied to the back of the substrate to an extent sufficient to cause the thermoplastic material to melt. This seals the substrate by bonding the strands together, secures the pile strips in place, and prevents fraying of the substrate when it is subsequently slit. Heat sealing can be easily accomplished by passing the substrate over a heated rod, such as a brass rod, at a temperature between 440.degree. and 460.degree. F., for example, at a speed of 3.1 ft. per minute.
It will be appreciated that the foregoing and other details of the method for manufacturing weatherstrips of the type herein described are exemplary only, and per se form no particular part of this invention except in combination with the novel aspects hereof.
Weatherstrips of the type described, although providing salutory performance in a variety of applications for many years, nevertheless suffer from several disadvantages. Often, when long lengths of weatherstrip are installed in a T-slot or similar mounting structure, the sliding friction between the backing strip and the surface of the T-slot make installation difficult. While lubricants can be employed to reduce the friction, they are often messy, and complicate the installation process.
A second problem arises during manufacture of the weatherstrips. As described above, the weatherstrips are preferably made in batches on a wide substrate, and subsequently slit into individual strips. It is a requirement of efficient manufacture that the slitting operation be carried out at high speeds, while maintaining accurate longitudinal alignment with the sealing bodies, so that a weatherstrip is produced in which the sealing body is centered and straight with respect to the backing strip. It is an advantage if the slitting operation can be carried out at high speed, since this reduces the cost of the product.
Maintaining accurate alignment has heretofore been a problem and in many instances, trimming operations have been required following separation of the web into individual weatherstrips, to achieve the necessary tolerances.
Still further, the speed of manufacture of weatherstrips of the type described herein is also related to the time that it takes for the extruded or melted portion of the backing strip to cool and become dimensionally stable. The strip cannot be cut until the substrate has cooled, and this is often a limiting factor in the speed of manufacture.
Because the weatherstrips to which this invention relates are manufactured and used in large quantities, cost is always a consideration. The cost of materials is a significant portion of the total cost of the weatherstrip, and reducing the amount of material required to manufacture the weatherstrip is an important consideration in keeping the cost low.
Accordingly, it is an object of this invention to provide a weatherstrip that addresses these and other problems of prior art for weatherstrips, and provides an improved weatherstrip in which frictional forces between the weatherstrips and the mounting slot that impede installation are reduced; in which the strip is substantially self-aligning during cutting, so that higher speeds and yields may be achieved; in which the cooling time for the thermoplastic backing material is reduced; and in which the amount of polypropylene backing material required to form the weatherstrip is reduced.
Briefly stated, in accordance with the presently preferred embodiment of this invention, an improved weatherstrip includes a longitudinally extending backing strip, having a front surface and a rear surface; a sealing body attached to the front surface of the backing strip; and a plurality of longitudinally extending grooves formed in the rear surface of the backing strip for reducing the frictional forces between the backing strip and a mounting slot, increasing the surface area for speeding the cooling of the backing strip during manufacture, and for aligning the strip during slitting.
In accordance with another aspect of this invention, the grooves described above are provided having a depth less than half the overall thickness of the backing strip.
In accordance with yet another aspect of this invention, the grooves have a generally V-shaped section, in which the peak-to-peak spacing is greater than the depth of the grooves.
In accordance with still another aspect of this invention, the backing strip comprises a layer of fabric and a layer of thermoplastic material on the layer of fabric.
In accordance with a still further embodiment of this invention, the layer of thermoplastic material is a polypropylene resin layer.
A method for manufacturing a weatherstrip in accordance with this invention includes the steps of weaving strands of an appropriate material to form a substrate, knitting or weaving or otherwise inserting filaments of pile material through the substrate or attaching an alternate sealing body at spaced locations along the substrate; extruding a coating of polypropylene resin onto the surface of the substrate opposite the sealing body; cooling the extruded backing material to the point where the material sets without further flow; and embossing or cutting a plurality of parallel grooves onto said backing strip in a direction parallel to the longitudinal extent of the weatherstrips.